TAMPA — Suncoast residents will finally begin to see a return on the tens of millions of dollars they paid to repair a reservoir that began leaking shortly after it was built.

Work on the C.W. Bill Young Regional Reservoir is nearing completion, Tampa Bay Water officials said Thursday. And this time, extra steps have been taken to prevent the drainage problems that led the regional wholesaler to empty, gut and repair the 15.5 billion-gallon facility in the first place.

After more than a year and $129 million in repairs, the reservoir now has a new, high-performance liner, a 9-inch thick layer of drainage rock that will allow water to flow under a new erosion-control layer, and seven, 40-foot tall aeration towers to circulate and pump oxygen into the stored water.

The builder, Kiewit Infrastructure South Co., will stay under contract with Tampa Bay Water for five years, or two of the reservoir’s fill cycles, officials said.

The reservoir is expected to be completely finished by December, maybe earlier, officials said. All that remains to be done is to complete the seawall and aeration towers and pave some of the areas around the edge of the basin.

Water from the Alafia River and Tampa Bay Bypass Canal already is being pumped into the reservoir at a rate of 130 million gallons per day, officials said. Depending on the rain this year, they expect the massive structure to be completely full by next summer.

Tampa Bay Water provides drinking water to more than 2.3 million residents in Hillsborough, Pinellas and Pasco counties. The utility built the above-ground reservoir — the largest in the state — in 2005 to supplement its underground wells and desalination plant on Cockroach Bay.

But about 18 months after construction was complete, deep cracks began forming in the 50-foot walls. The cracks — some of them hundreds of feet long — started along the basin’s upper edge and eventually spread about two-thirds of the way down the soil-and-concrete lining in the reservoir’s sloped sides.

Tampa Bay Water blamed the contractors that worked on the reservoir, including Nebraska-based HDR Engineering, for the leaks. The other contractors settled out of court, but in 2011, Tampa Bay Water rejected a $30 million settlement and opted for a jury trial in a bid to sue HDR for more than $100 million.

Tampa Bay Water lost the suit in 2012 and was ordered to cover HDR’s $20 million in legal fees. That left the utility’s customers responsible for the costs to drain and repair the reservoir.

Workers ripped up the soil cement within the 5 miles of the basin’s interior walls and hauled it away. Kiewit installed a drainage system and added more dirt — called a soil wedge — under a thicker, stronger layer of soil-cement to control erosion.

In the original design, the water wasn’t draining from under the erosion-control lining, Carden said. Now, the reservoir has a thick layer of crushed stone on top of the new liner that allows the water to flow out beneath the soil cement.

“No pressure, no more cracks,” Carden said.

The reservoir was renovated from the bottom up, so the company could begin funneling in water while workers put the finishing touches on the outer edge, Carden said.

“We wanted to take advantage of the rainy season,” he said.

The reservoir stores surplus water from the river and the canal, and will serve as the area’s “water savings account,” officials said. If needed, the water will pass from the reservoir to the water treatment plant and on to the city water systems.

“It can take quite a long time to drain this down if we use it conservatively,” Carden said.

The reservoir is a “vital infrastructure” that will provide water to Tampa Bay Water customers during the dry season and droughts, said Matt Jordan, the company’s general manager.

“We’re in a much better position once the reservoir is full,” Jordan said.